var context;
var arr = new Array();
var starCount = 1600;
var rains = new Array();
var rainCount = 25;
//初始化画布及context
function init() {
  //获取canvas
  var stars = document.getElementById("stars");
  windowWidth = window.innerWidth; //当前的窗口的高度
  stars.width = windowWidth;
  stars.height = window.innerHeight;
  //获取context
  context = stars.getContext("2d");
}
//创建一个星星对象
var Star = function () {
  this.x = windowWidth * Math.random(); //横坐标
  this.y = 5000 * Math.random(); //纵坐标
  this.text = "."; //文本
  this.color = "white"; //颜色
  //产生随机颜色
  this.getColor = function () {
    var _r = Math.random();
    if (_r < 0.5) {
      this.color = "#333";
    } else {
      this.color = "white";
    }
  }
  //初始化
  this.init = function () {
    this.getColor();
  }
  //绘制
  this.draw = function () {
    context.fillStyle = this.color;
    context.fillText(this.text, this.x, this.y);
  }
}
//页面加载的时候
window.onload = function () {
  init();
  //画星星
  for (var i = 0; i < starCount; i++) {
    var star = new Star();
    star.init();
    star.draw();
    arr.push(star);
  }
  //画流星
  for (var i = 0; i < rainCount; i++) {
    var rain = new MeteorRain();
    rain.init();
    rain.draw();
    rains.push(rain);
  }
  playStars(); //绘制闪动的星星
  playRains(); //绘制流星

}
//星星闪起来
function playStars() {
  for (var n = 0; n < starCount; n++) {
    arr[n].getColor();
    arr[n].draw();
  }

  setTimeout("playStars()", 100);
}

/*流星雨开始*/
var MeteorRain = function () {
  this.x = -1;
  this.y = -1;
  this.length = -1; //长度
  this.angle = 30; //倾斜角度
  this.width = -1; //宽度
  this.height = -1; //高度
  this.speed = 1; //速度
  this.offset_x = -1; //横轴移动偏移量
  this.offset_y = -1; //纵轴移动偏移量
  this.alpha = 1; //透明度
  this.color1 = ""; //流星的色彩
  this.color2 = ""; //流星的色彩
  /****************初始化函数********************/
  this.init = function () //初始化
  {
    this.getPos();
    this.alpha = 1; //透明度
    this.getRandomColor();
    //最小长度，最大长度
    var x = Math.random() * 80 + 150;
    this.length = Math.ceil(x);
    //         x = Math.random()*10+30;
    this.angle = 30; //流星倾斜角
    x = Math.random() + 0.5;
    this.speed = Math.ceil(x); //流星的速度
    var cos = Math.cos(this.angle * 3.14 / 180);
    var sin = Math.sin(this.angle * 3.14 / 180);
    this.width = this.length * cos; //流星所占宽度
    this.height = this.length * sin; //流星所占高度
    this.offset_x = this.speed * cos;
    this.offset_y = this.speed * sin;
  }
  /**************获取随机颜色函数*****************/
  this.getRandomColor = function () {
    var a = Math.ceil(255 - 240 * Math.random());
    //中段颜色
    this.color1 = "rgba(" + a + "," + a + "," + a + ",1)";
    //结束颜色
    this.color2 = "black";
  }
  /***************重新计算流星坐标的函数******************/
  this.countPos = function () //
  {
    //往左下移动,x减少，y增加
    this.x = this.x - this.offset_x;
    this.y = this.y + this.offset_y;
  }
  /*****************获取随机坐标的函数*****************/
  this.getPos = function () //
  {
    //横坐标200--1200
    this.x = Math.random() * window.innerWidth; //窗口高度
    //纵坐标小于600
    this.y = Math.random() * window.innerHeight; //窗口宽度
  }
  /****绘制流星***************************/
  this.draw = function () //绘制一个流星的函数
  {
    context.save();
    context.beginPath();
    context.lineWidth = 1; //宽度
    context.globalAlpha = this.alpha; //设置透明度
    //创建横向渐变颜色,起点坐标至终点坐标
    var line = context.createLinearGradient(this.x, this.y,
      this.x + this.width,
      this.y - this.height);
    //分段设置颜色
    line.addColorStop(0, "white");
    line.addColorStop(0.3, this.color1);
    line.addColorStop(0.6, this.color2);
    context.strokeStyle = line;
    //起点
    context.moveTo(this.x, this.y);
    //终点
    context.lineTo(this.x + this.width, this.y - this.height);
    context.closePath();
    context.stroke();
    context.restore();
  }
  this.move = function () {
    //清空流星像素
    var x = this.x + this.width - this.offset_x;
    var y = this.y - this.height;
    context.clearRect(x - 3, y - 3, this.offset_x + 5, this.offset_y + 5);
    //         context.strokeStyle="red";
    //         context.strokeRect(x,y-1,this.offset_x+1,this.offset_y+1);
    //重新计算位置，往左下移动
    this.countPos();
    //透明度增加
    this.alpha -= 0.002;
    //重绘
    this.draw();
  }
}
//绘制流星
function playRains() {
  for (var n = 0; n < rainCount; n++) {
    var rain = rains[n];
    rain.move(); //移动
    if (rain.y > window.innerHeight) { //超出界限后重来
      context.clearRect(rain.x, rain.y - rain.height, rain.width, rain.height);
      rains[n] = new MeteorRain();
      rains[n].init();
    }
  }
  setTimeout("playRains()", 2);
}
/*流星雨结束*/
